1. Field of the Invention
The present invention relates to a force/moment sensor for measurement of particularly three orthogonal forces and three orthogonal moments.
2. Description of the Prior Art
For measurement of three forces and three moments, a monolithic force/moment sensor is known from DE 102 17 018. This known sensor comprises two circular cylindrical rings arranged at an axial distance from each other. The two rings are connected to each other via six rods of identical length which are distributed along the periphery at uniform intervals. On said rods, strain gauges are arranged. With the aid of the strain gauges, three orthogonal forces and three orthogonal moments can be determined. The connection between the six rods and the two circular cylindrical rings is realized respectively via flexure hinges. The strain gauges are connected via electric lines to an evaluation unit for determining the forces and moments. Such a force/moment sensor, however, has the disadvantage that the manufacture as a monolithic component is extremely complex and thus expensive. Further, such a force/moment sensor has a large size particularly in the axial direction so that the range of applications of such a force/moment sensor is restricted.
A relatively flat-sized force/moment sensor from ATI Industrial Automation, Apex, N.C., USA, available under the trade name ATI-Nano 43, is schematically shown in FIG. 1. This sensor comprises an outer holding element 10 surrounding an inner holding element 20. The two holding elements 10,20 are connected to the respective components between which the occurring forces and moments shall be measured. The two holding elements are connected to each other via three deformation elements 12. The deformation elements 12 comprise a first component in the form of a beam having a substantially quadratic cross section. Via a support member 16, said beam is connected, at the ends 18 of support member 16, to the outer holding element 10. On the top and bottom sides 22 and the two lateral surfaces 24 of the beam 12, a respective strain gauge 26 is arranged. Since the force/moment sensor shown in FIG. 1 comprises three deformation elements arranged at regular intervals on the periphery of the inner holding element 20, this results in a total of twelve deformation transducers in the form of the strain gauges 26. The above arrangement allows for the detection of three forces and three moments. Particularly when using such a sensor in surgical instruments, a central opening 28 is important for allowing instruments and other components to be passed through. On the other hand, the outer dimensions of the sensor should be as small as possible. For this reason, a miniaturization of such a force/moment sensor to an outer diameter of less than 20 mm is not possible, particularly because of the need to provide sufficient mounting space for the strain gauge arranged laterally on the beam 14. Also, the problem exists that a still further reduction of the material volume at the clamping points might cause a twisting of the structure, which would impair the measurement results.
From DE 102 17 019, a further monolithic force/moment sensor is known. An inner holding element is connected via three strut-shaped deformation elements to three outer holding elements. The outer holding elements extend between the outer ends of the substantially radially arranged strut-shaped deformation elements. Different deformation transducers, such as e.g. strain gauges, for capturing linear forces or shear forces, are arranged both on the top sides of the deformation elements and on the three outer holding elements. Thus, the outer elements serve, on the one hand, as holding elements for holding the sensor and, on the other hand, also as deformation elements, since it is only by deformation of these elements that corresponding forces can be detected via the deformation transducers. This particularly has the disadvantage that, when the force/moment sensor is mounted, the attachment process may cause tension at the outer holding elements. Thereby, the measurement results may be adversely affected.
From DE 100 13 059, there is further known a force/moment sensor with an outer holding element and an inner holding element. Provided on the inner holding element is a stamp extending in the longitudinal direction and serving to accommodate the corresponding deformation transducer elements. Further, deformation transducer elements are provided both on the upper side and on the lower side of the outer holding element. Also in this force/moment sensor, the measurement results may be affected due to the tension occurring when the sensor is being fastened.
It is an object of the invention to provide a force/moment sensor which is suited particularly for the measurement of three preferably orthogonal forces and three preferably orthogonal moments, and which is simple in construction so as to allow particularly for strong miniaturization.
According to the invention, the above object is achieved by the features as disclosed herein.